The vertical diameters are: 1. The mento-bregmatic, M. B., from the chin to the centre of the great fontanelle; it measures 4.4 inches.
2. The trachelo-bregmatic, Tr.B., or sub-mento-bregmatic, S.M.B., traverses the head perpendicularly, from the bregma to the anterior part of the occipital foramen; it measures 3.8 inches.
The transverse diameters are: 1. The bi-parietal, B.P., the maximum transverse diameter of Bud in, goes from one parietal tuberosity to the other, an .1 measures 3.8 inches.
2. The bi-temporal, B.T., the minimum transverse diameter, extends from the point of beginning of the parieto-frontal suture of one side to a similar point upon the other side. It is 3.2 inches long.
The bi-mastoid stretches from the one mastoid process to the other. It measures 3 inches (Figs. 168, 169).
These dimensions are those of the undeformed head; but during its passage through the pelvis the festal occiput undergoes certain modifica tions to which Budin has called attention. Those modifications are normal. After having studied and compared the results of English and German investigators, Budin arrives at the following conclusions: Under the influence of the compression of the head by the pelvis, there occurs a sliding and overriding of the bones at the sutures, so as to pro duce a deformity varying with the different presentations. To this we
will return later; but the following points may be here noted: In vertex presentations, diminution of the diameters O.M. and 0.F; Increase of the maximum diameter sub. 0.M; Diminution of the sub-O.Breg. and B.T. diameters; Diminution less pronounced, of the diameter B.P; Irreducibility of the bi-mastoid diameter.
These ideas differ, as is evident, from those heretofore held.
In breech presentations—little or no modification of the head. In face presentations, increase of the diameters 0.M. and 0.F. Decrease of the diameters M. Breg. and S.M.B.
In the trunk he distinguishes the following diameters: Bi-acromial . . 4.4 inches.
Sterno-dorsal • 3.8 " Bi-iliac . 3.2 " Bi-trochanteric . . 3.6 "